1. Field of the Invention
The present invention relates generally to a pulse wave detecting apparatus, and more particularly to an apparatus capable of highly accurate detection of a pulse wave based on pulsations of an arterial vessel.
2. Discussion of the Prior Art
Blood pressure pulsations which are produced by heartbeats of a living being and which propagate through arteries, or pulsations of the arterial vessel walls, are generally referred to simply as "pulse wave". It is known in the art that detecting such a pulse wave of a living body provides various medical information such as a working condition of the heart of the living being. To detect the pulse wave, there is available a detecting apparatus which has a presser or contractor member which is pressed against a portion of a skin or epidermal tissue of the human being which is right above an arterial vessel. The pressure member has a contact element which is vibrated due to blood pressure pulsations of the arterial vessel. The detecting apparatus includes a converter such as a strain gauge or piezoelectric element, which converts the vibrations of the contact element caused by the pulsations of the arterial vessel, into electric signals as an output of the apparatus. An example of this type of detecting apparatus is disclosed in laid-open publication No. 61-60901 of Japanese Utility Model Application.
The contact element of the presser member of the detecting apparatus indicated above must be accurately positioned in place right above the artery, in order that the pulse wave is sensed with a high level of precision. Usually, the positioning of the contact element on the human being is manually conducted by an operator, who holds the frame or support structure holding the presser member, and places the frame into position on the appropriate portion of the human being, by way of visual inspection. This procedure does not necessarily permit the contact element to be exactly positioned right above the arterial vessel. Alternatively, the presser member is provided with a plurality of contact elements each of which is sufficiently smaller in size than the diameter of the arterial vessel. In this case, the detecting apparatus is positioned such that the contact elements are arranged in a direction perpendicular to the vessel. In operation, the most optimally located one of the contact elements is selected based on the vibrating conditions of the individual contact elements. In this case, it is difficult to manufacture the pressure member with the relatively small contact elements, and the converter which is required to convert the vibrations of all the contact elements into electric signals. Further, the sensitivity of the detecting apparatus is lowered as the size of the converter is reduced.